View LTC3100_4319599.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

FEATURES
n n n n n
LTC3100 1.5MHz Synchronous Dual Channel DC/DC Converter and 100mA LDO DESCRIPTION
The LTC(R)3100 combines a high efficiency 700mA synchronous step-up converter, a 250mA synchronous step-down converter and a 100mA LDO regulator. The LTC3100 features a wide input voltage range of 0.65V to 5V. The step-down converter can be powered by the output of the step-up converter or from a separate power source between 1.8V and 5.5V. The LDO can also be used as a sequencing switch on the output of the boost. A switching frequency of 1.5MHz minimizes solution footprint by allowing the use of tiny, low profile inductors and ceramic capacitors. The switching regulators use current mode control and are internally compensated, reducing external parts count. Each converter automatically transitions to Burst Mode operation to maintain high efficiency over the full load range. Burst Mode operation can be disabled for low noise applications. The integrated LDO provides a third low noise, low dropout supply. Anti-ringing circuitry reduces EMI by damping the boost inductor in discontinuous mode. Additional features include shutdown current of under 1A and overtemperature shutdown. The LTC3100 is housed in a 16-lead 3mm x 3mm 0.75mm QFN package.
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
n
n
n
Extremely Compact Triple-Rail Solution Burst Mode(R) Operation, IQ = 15A 1.5MHz Fixed Frequency Operation Power Good Indicators 700mA Synchronous Step-Up DC/DC 0.65V to 5V VIN Range 1.5V to 5.25V VOUT Range 94% Peak Efficiency VIN > VOUT Operation Output Disconnect 250mA Synchronous Step-Down DC/DC 1.8V to 5.5V VIN Range 0.6V to 5.5V VOUT Range LDO (VIN Internally Tied to VBST) 0.6V to 5.25V VOUT Range 200mV Dropout Voltage at 100mA Available in a 16-Lead 3mm x 3mm QFN Package
APPLICATIONS
n n n
Bar Code Readers Medical Instruments Low Power Portable Electronic Devices
TYPICAL APPLICATION
Two-Cell, Triple Output Converter
3.3H VBATT 1.6V TO 3.2V 2.2F LTC3100 PGBST VLDO 102k FBLDO FF EN_BURST BOOST LDO BUCK OFF ON OFF ON OFF ON MODE 4.7H RUNBST RUNLDO RUNBK GND SWBK 2M FBBK 1M PGBK
3100 TA01a
3.3V AT 100mA VBOOST SWBST VINBK VBST FBBST 1.07M BOOST_GOOD 3V AT 50mA VLDO 2.2F EFFICIENCY (%) 1.87M 10F 2 1M
Efficiency and Power Loss vs Load Current, VIN = 2.4V
100 90 80 70 60 50 40 30 BOOST BUCK PL, BOOST PL, BUCK 0.1 1 10 100 LOAD CURRENT (mA) 1 10 100 POWER LOSS (mW) 1000
VINBST
25.5k 1.8V AT 200mA VBUCK 10F 1M
20 10 0 0.01
0.1
0.01 1000
3100 TA01b
BUCK_GOOD
3100fa
1
LTC3100 ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW RUNBST PGBST VINBST MODE 12 FBBST 11 FBLDO 17 10 RUNLDO 9 5 VINBK 6 PGBK 7 GND 8 RUNBK FBBK
VINBST and VINBK Voltage .............................. -0.3 to 6V SWBST, SWBK DC Voltage ............................. -0.3 to 6V SWBST, SWBK Pulsed (< 100ns) Voltage ...... -0.3 to 7V FBBST, FBBK, FBLDO, PGBST, PGBK Voltage . -0.3 to 6V MODE, RUNBST, RUNBK, RUNLDO Voltage ... -0.3 to 6V VBST, VLDO ...................................................... -0.3 to 6V Operating Temperature (Notes 2, 5) .........-40C to 85C Storage Temperature Range...................-65C to 125C
16 15 14 13 SWBST 1 VBST 2 VLDO 3 SWBK 4
UD PACKAGE 16-LEAD (3mm 3mm) PLASTIC QFN TJMAX = 125C, JA = 68C/W, 4-LAYER BOARD EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB (NOTE 6)
ORDER INFORMATION
LEAD FREE FINISH LTC3100EUD#PBF TAPE AND REEL LTC3100EUD#TRPBF PART MARKING LDJR PACKAGE DESCRIPTION 16-Lead (3mm x 3mm) Plastic QFN TEMPERATURE RANGE -40C to 85C Consult LTC Marketing for parts specified with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based finish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS: STEP-UP CONVERTER
PARAMETER Minimum Start-Up Voltage Input Voltage Range Output Voltage Adjust Range Feedback Voltage Feedback Input Current Quiescent Current (VIN): Shutdown Quiescent Current: Active Quiescent Current: Burst Mode Operation N-Channel MOSFET Switch Leakage Current P-Channel MOSFET Switch Leakage Current FBBST = 1.2V RUNBST = 0V, Not Including Switch Leakage, VBST = 0V, VINBK = 0V Measured on VBST (Note 4), RUNBK = 0V, RUNLDO = 0V Measured on VBST, FBBST > 1.25V MODE = 1V, RUNLDO = 0V MODE = 1V, RUNLDO = 1V SWBST = 5V, VBST= 5V SWBST = 0V, VBST = 5V CONDITIONS ILOAD = 1mA After Start-Up (Minimum Voltage Is Load Dependent)
l l l l
The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: -40C to 85C, VINBST = 1.2V, VBST = 3.3V, TA = 25C, unless otherwise noted.
MIN 0.5 1.5 1.182 1.200 1 0.01 300 15 28 0.1 0.1 TYP 0.65 MAX 0.90 5 5.25 1.218 50 1 500 25 45 5 10 UNITS V V V V nA A A A A A A
3100fa
2
LTC3100 ELECTRICAL CHARACTERISTICS: STEP-UP CONVERTER
PARAMETER N-Channel MOSFET Switch-On Resistance P-Channel MOSFET Switch-On Resistance N-Channel MOSFET Current Limit Maximum Duty Cycle Minimum Duty Cycle Switching Frequency RUNBST Input High Voltage RUNBST Input Low Voltage RUNBST Input Current Soft-Start Time PGBST Threshold, Falling PGBST Hysteresis PGBST Voltage Low PGBST Leakage Current Referenced to Feedback Voltage Referenced to Feedback Voltage 5mA Load PGBST = 5.5V RUNBST = 1.2V VFBBST = 1.15V VFBBST = 1.3V CONDITIONS VBST = 3.3V VBST = 3.3V
l l l l l l
The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: -40C to 85C, VINBST = 1.2V, VBST = 3.3V, TA = 25C, unless otherwise noted.
MIN TYP 0.3 0.4 700 87 1.2 0.9 0.3 0.8 0.8 -8 3 65 0.01 10 2 850 90 0 1.5 1.8 MAX UNITS mA % % MHz V V A ms % % mV A
ELECTRICAL CHARACTERISTICS: STEP-DOWN CONVERTER
PARAMETER Input Voltage Range Output Voltage Adjust Range Feedback Voltage Feedback Input Current Quiescent Current: Shutdown Quiescent Current: Active Quiescent Current: Burst Mode Operation N-Channel MOSFET Switch Leakage Current P-Channel MOSFET Switch Leakage Current N-Channel MOSFET Switch-On Resistance P-Channel MOSFET Switch-On Resistance P-Channel MOSFET Current Limit Maximum Duty Cycle Minimum Duty Cycle Switching Frequency FBBK < 590mV FBBK > 610mV FBBK = 600mV Measured on VINBK, RUNBK = 0V, VINBST = 0V, VBST = 0V Not Including Switch Leakage Measured on VINBK (Note 4), RUNBST = 0V Measured on VINBK, FBBK = 620mV, MODE = OPEN, RUNBST = 0V VINBK = SWBK = 5V SWBK = 0V, VINBK = 5V VINBK = 3.3V VINBK = 3.3V
l l l l
The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: -40C to 85C, VINBK = 3.3V, TA = 25C, unless otherwise noted.
CONDITIONS
l l l
MIN 1.8 0.61 590
TYP
MAX 5.5 5.5
UNITS V V mV nA A A A A A mA %
600 1 0.01 240 16 0.1 0.1 0.45 0.55
610 30 1 350 30 5 5
340 100
450 0
% MHz
1.2
1.5
1.8
3100fa
3
LTC3100 ELECTRICAL CHARACTERISTICS: STEP-DOWN CONVERTER
PARAMETER RUNBK Input High Voltage RUNBK Input Low Voltage RUNBK Input Current Soft-Start Time PGBK Threshold, Falling PGBK Hysteresis PGBK Voltage Low PGBK Leakage Current Referenced to Feedback Voltage Referenced to Feedback Voltage 5mA Load PGBK = 5.5V RUNBK = 1.2V CONDITIONS
l l
The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: -40C to 85C, VINBK = 3.3V, TA = 25C, unless otherwise noted.
MIN 0.9 0.3 0.8 1.3 -8 3 65 0.01 10 2 TYP MAX UNITS V V A ms % % mV A
ELECTRICAL CHARACTERISTICS: LDO REGULATOR
PARAMETER Input Voltage Range Output Voltage Adjust Range Feedback Voltage Maximum Output Current Feedback Input Current Line Regulation Load Regulation Dropout Voltage Ripple Rejection (PSRR) Short-Circuit Current Limit Soft-Start Time RUNLDO Input High Voltage RUNLDO Input Low Voltage RUNLDO Input Current Quiescent Current--Active RUNLDO = 1.2V RUNLDO = 3.3V, Measured on VBST RUNBST = RUNBK = 0V, VINBK = 0V FBLDO = 600mV VIN = 3.3V to 5.25V From 10mA to 100mA Load IOUT = 100mA Frequency = 1.5MHz at ILOAD = 50mA, COUT = 2.2F (Note 3) FBLDO < 582mV (Note 3) CONDITIONS
The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: -40C to 85C, VBST = 3.3V, VLDO = 3V, TA = 25C, unless otherwise noted.
MIN
l l l l
TYP
MAX 5.25 5.25
UNITS V V mV mA nA %/ V %
1.8 0.618 582 100 600 120 1 0.1 0.1
618 30
l l l l
130 35 120 0.3 0.9
200 160
mV dB mA ms V
0.3 0.8 26 2 40
V A A
ELECTRICAL CHARACTERISTICS: COMMON CIRCUITRY
PARAMETER MODE Input High Voltage MODE Input Low Voltage MODE Input Current MODE = 0V MODE = 5V CONDITIONS
l l
The l denotes the specifications which apply over the full operating temperature range. Extended commercial grade: -40C to 85C, VBST or VINBK = 3.3V, TA = 25C, unless otherwise noted.
MIN 0.9 0.3 -3.3 1.7 -5 3 TYP MAX UNITS V V A A
3100fa
4
LTC3100 ELECTRICAL CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The LTC3100E is guaranteed to meet performance specifications from 0C to 85C. Specifications over -40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Specification is guaranteed by design and not 100% tested in production. Note 4: Current measurements are made when the output is not switching. Note 5: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may result in device degradation or failure. Note 6: Failure to solder the exposed backside of the package to the PC board ground plane will result in a thermal resistance much higher than 68C/W.
TYPICAL PERFORMANCE CHARACTERISTICS
Step-Up DC/DC Converter Efficiency vs Load Current and VIN for VO = 1.8V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 VIN = 1.2V VIN = 1.5V PL, VIN = 1.2V PL, VIN = 1.5V 1 10 100 LOAD CURRENT (mA) 0.1 1 10 100 POWER LOSS (mW) EFFICIENCY (%) 1000 100 90 80 70 60 50 40 30 20 10 0 0.01
TA = 25C, unless otherwise specified.
Efficiency vs Load Current and VIN for VO = 3.3V
1000
100 POWER LOSS (mW)
10
1 VIN = 1.2V VIN = 2.4V VIN = 3V PL, VIN = 1.2V PL, VIN = 2.4V PL, VIN = 3V 0.1 1 10 100 LOAD CURRENT (mA)
0.1
0.01 1000
0.01 1000
3100 G01
3100 G02
Efficiency vs Load Current and VIN for VO = 5V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 VIN = 1.8V VIN = 2.4V VIN = 3.6V PL, VIN = 1.8V PL, VIN = 2.4V PL, VIN = 3.6V 1 10 100 LOAD CURRENT (mA) 1 10 100 POWER LOSS (mW) EFFICIENCY (%) 1000 100 90 80 70 60 50 40 30 20 10
3.3V, 100mA Efficiency vs VIN
0.1
0.01 1000
VBST = 3.3V AT 100mA 0 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 4.2 VINBST (V)
3100 G04
3100 G03
3100fa
5
LTC3100 TYPICAL PERFORMANCE CHARACTERISTICS
Step-Up DC/DC Converter No-Load Input Current vs VIN, Mode = Open, LDO and Buck Off
180 160 OUTPUT CURRENT (mA) 140 INPUT CURRENT (A) 120 100 80 60 40 20 0 1.0 1.5 2.0 2.5 3.0 VINBST (V) 3.5 4.0 4.5 VOUT = 1.8V VOUT = 3.3V 0 0 0.5 1 1.5 2.5 3 VINBST (V) 2 3.5 4 4.5 1 0.7 0.8 0.9 1 1.1 VINBST (V) 1.2 1.3
3100 G07
TA = 25C, unless otherwise specified.
Maximum Output Current vs VIN
600 500 LOAD CURRENT (mA)
3100 G06
Maximum Load Current During Start-Up vs VIN
1000
VOUT = 3.3V
VOUT = 1.8V 400 300 VOUT = 5V 200 100
100
10
VOUT = 5V
3100 G05
VBST = 1.8V, RESISTIVE LOAD VBST = 1.8V, CONSTANT-CURRENT LOAD VBST = 3.3V, RESISTIVE LOAD VBST = 3.3V, CONSTANT-CURRENT LOAD VBST = 5V, RESISTIVE LOAD VBST = 5V, CONSTANT-CURRENT LOAD
Burst Mode Threshold Current vs VIN
60 50 LOAD CURRENT (mA) 40 30 VOUT = 5V 20 10 0 1.0 VOUT = 3.3V VOUT = 1.8V INPUT VOLTAGE (V) L = 3.3H 0.85 0.80 0.75 0.70 0.65 0.60 0.55
Start-Up Voltage vs Temperature
1.5
2.0
2.5 3.0 VINBST (V)
3.5
4.0
4.5
0.50 -45 -30 -15
0 15 30 45 60 TEMPERATURE (C)
75
90
3100 G09
3100 G08
VOUT and IIN During Soft-Start
Output Voltage Ripple in Fixed Frequency and Burst Mode Operation
VBST COUT = 20F 0.5s/DIV 100mA LOAD 20mV/DIV
IIN 200mA/DIV
VBST 1V/DIV 500s/DIV
3100 G10
20s/DIV 5mA LOAD 20mV/DIV
3100 G11
3100fa
6
LTC3100 TYPICAL PERFORMANCE CHARACTERISTICS
Step-Up DC/DC Converter Load Step Response, 50mA-150mA Fixed Frequency Mode
VBST COUT = 10F IOUT 100mA/DIV IOUT 100mA/DIV
TA = 25C, unless otherwise specified.
Load Step Response, 5mA-100mA Burst Mode Operation Enabled
VBST COUT = 20F
VBST 50mV/DIV
VBST 50mV/DIV
100s/DIV
3100 G12
100s/DIV
3100 G13
LDO Regulator Dropout Voltage vs VOUT and Temperature (IOUT = 100mA)
0.250 DROPOUT VOLTAGE (VBST_VLDO) 0.225 0.200 VLDO = 2.5V PSRR (dB) 0.175 0.150 0.125 0.100 0.075 VLDO = 3.3V VLDO = 5V 10 VOUT = 3V 5I OUT = 50mA COUT = 2.2F 0 0.1 1 VLDO = 1.5V 40 35 30 25 20 15 VLDO 1V/DIV 100s/DIV
3100 G16
Ripple Rejection
Soft-Start Time
LDO COUT = 2.2F
RUNLDO 2V/DIV
0.050 -45 -30 -15
0
15
30
45
60
75
90
TEMPERATURE (C)
6105 G14
10 100 FREQUENCY (Hz)
1000
10000
3100 G15
Burst Mode Operation Ripple Rejection
LDO COUT = 2.2F BOOST RIPPLE 20mV/DIV
Load Step Response, 10mA-60mA
LDO COUT = 2.2F
50mA/DIV VLDO 100mV/DIV
LDO RIPPLE 20mV/DIV
5s/DIV
3100 G17
200s/DIV
3100 G18
3100fa
7
LTC3100 TYPICAL PERFORMANCE CHARACTERISTICS
Step-Down DC/DC Converter Efficiency vs Load Current and VIN for VO = 1.2V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.01 0.1 VIN = 1.8V VIN = 2.4V VIN = 3.3V PL, VIN = 1.8V PL, VIN = 2.4V PL, VIN = 3.3V 1 10 100 LOAD CURRENT (mA) 1 10 100 POWER LOSS (mW) EFFICIENCY (%) 1000 100 90 80 70 60 50 40 30 20 10 0 0.01 0.1 VIN = 2.4V VIN = 3.3V VIN = 5V PL, VIN = 2.4V PL, VIN = 3.3V PL, VIN = 5V 1 10 100 LOAD CURRENT (mA) 1 10 100 POWER LOSS (mW)
TA = 25C, unless otherwise specified.
Efficiency vs Load Current and VIN for VO = 1.8V
1000
0.1
0.1
0.01 1000
0.01 1000
3100 G19
3100 G20
No-Load Input Current vs VINBK (Mode = Open)
20 80 70 INPUT CURRENT (A) LOAD CURRENT (mA) 15 60 50 40 30 20 10 0 1.5 2 2.5 3 3.5 4 4.5
3100 G21
Burst Mode Operation Threshold Current vs VIN
VOUT = 1.2V INPUT CURRENT 50mA/DIV VOUT = 1.5V VOUT 0.5V/DIV VOUT = 1.8V VOUT = 2.5V
VOUT and IIN During Soft-Start
STARTUP 200mA LOAD , VIN = 2.4V VOUT = 1.2V COUT = 10F
10
5
2ms/DIV
3100 G23
5
0 2 2.5 3 3.5 VINBK (V)
3100 G22
4
4.5
5
VINBK (V)
Output Voltage Ripple in Fixed Frequency and Burst Mode Operation
COUT = 10F
Load Step Response, Fixed Frequency Mode 10mA to 100mA
COUT = 10F
Load Step Response, Burst Mode Operation Enabled 10mA to 100mA
COUT = 10F
50mV/DIV
100mA/DIV
50mA/DIV
50mV/DIV 50mV/DIV 50mV/DIV
5s/DIV
3100 G24
200s/DIV
3100 G25
200s/DIV
3100 G26
3100fa
8
LTC3100 TYPICAL PERFORMANCE CHARACTERISTICS
RUN Pin Threshold Voltage
0.625 450 400 0.600 THRESHOLD (V) RISING DELAY TIME (s) 350 300 250 200 150 100 50 0.500 1 1.5 2 2.5 3 VIN (V)
3100 G27
TA = 25C, unless otherwise specified.
Start-Up Delay Times vs VIN
BUCK BOOST
0.575 FALLING
0.550
LDO
0.525
3.5
4
4.5
5
0 0.5
1
1.5
2
2.5
3
3.5
4
4.5
3100 G28
5
VIN (V)
PIN FUNCTIONS
SWBST (Pin 1): Switch Pin for the Boost Converter. Connect the boost inductor between SWBST and VINBST. Keep PCB trace lengths as short and wide as possible to reduce EMI. If the inductor current falls to zero, an internal anti-ringing switch is connected from SWBST to VINBST to minimize EMI. VBST (Pin 2): Output Voltage for the Boost Converter (which is the drain of the internal synchronous rectifier) and Input Voltage for the LDO. PCB trace length from VBST to the output filter capacitor (10F minimum) should be as short and wide as possible. VLDO (Pin 3): Output Voltage of the LDO Regulator. Connect a 1F ceramic capacitor between VLDO and GND. Larger values of capacitance may be used for higher PSRR or improved transient response. SWBK (Pin 4): Switch Pin for the Buck Converter. Connect the buck inductor between SWBK and the buck output filter capacitor. Keep PCB trace lengths as short and wide as possible to reduce EMI. VINBK (Pin 5): Input Voltage for the Buck Converter. Connect a minimum of 4.7F ceramic decoupling capacitor from this pin to ground. PGBK (Pin 6): Open-Drain Output That Pulls Low When FBBK Is More Than 8% Below Its Regulated Voltage. Connect a pull-up resistor from this pin to a positive supply less than 6V. GND (Pin 7): Signal Ground. Provide a short, direct PCB path between GND and the PC board ground plane connected to the Exposed Pad. RUNBK (Pin 8): Logic-Controlled Shutdown Input for the Buck Converter. There is an internal 4M pull-down on this pin. RUNBK = High: Normal operation RUNBK = Low: Shutdown FBBK (Pin 9): Feedback Input to the gm Error Amplifier for the Buck Converter. Connect the resistor divider tap to this pin. The output voltage can be adjusted from 0.6V to 5.5V by: R6 VOUT _ BUCK = 0 . 600 V * 1 + R5 RUNLDO (Pin 10): Logic-Controlled Shutdown Input for the LDO Regulator. There is an internal 4M pull-down on this pin. RUNLDO = High: Normal operation RUNLDO = Low: Shutdown
3100fa
9
LTC3100 PIN FUNCTIONS
FBLDO (Pin 11): Feedback Input to the gm Error Amplifier for the LDO Regulator. Connect the resistor divider tap to this pin. The output voltage can be adjusted from 0.6V to 5.25V by: R4 VOUT _ LDO = 0 . 600 V * 1 + R3 FBBST (Pin 12): Feedback Input to the gm Error Amplifier for the Boost Converter. Connect the resistor divider tap to this pin. The output voltage can be adjusted from 1.5V to 5.25V by: R2 VOUT _ BOOST = 1 . 20 V * 1 + R1 MODE (Pin 13): Logic-Controlled Mode Select Pin for Both the Boost and Buck Converters. There is an internal 1M pull-up on this pin to the higher of VINBST, VBST or VINBK. MODE = Float or High: Enables Burst Mode operation for both the boost and the buck. MODE = Low: Disables Burst Mode operation. Both converters will operate in fixed frequency mode regardless of load current. RUNBST (Pin 14): Logic-Controlled Shutdown Input for the Boost Converter. There is an internal 4M pull-down on this pin. RUNBST = High: Normal operation RUNBST = Low: Shutdown PGBST (Pin 15): Open-Drain Output That Pulls to Ground When FBBST Is More Than 8% Below Its Regulated Voltage. Connect a pull-up resistor from this pin to a positive supply less than 6V. VINBST (Pin 16): Input Voltage for the Boost Converter. Connect a minimum of 1F ceramic decoupling capacitor from this pin to ground. Exposed Pad (Pin 17): The Exposed Pad must be soldered to the PCB ground plane. It serves as the power ground connection, and as a means of conducting heat away from the die.
3100fa
10
LTC3100 BLOCK DIAGRAM
VBATT1, 0.65V TO 5V CIN 2.2F 16 VBST VINBST
L1, 3.3H
VBOOST, 1.5V TO 5.25V R2 1 SWBST 2 VBST FBBST 12 VSEL WELL SWITCH PGBST 15 R1 COUT 10F
VBEST VINBK VB GATE DRIVERS AND ANTI-CROSS CONDUCTION
VBEST
1.1V
VBEST OF 3 VREF VREF_GD VREF VREF_GD
-+
SLOPE COMPARATOR
IZERO COMPARATOR 0.15
WELL SWITCH
IPK COMPARATOR START_OSC IPK IZERO
START-UP
MODE CONTROL TSD BURST CLAMP
THERMAL SHUTDOWN RUNBST 14 OFF ON 4M SHUTDOWN
WAKE VBST 1M LEVEL SHIFT
MODE 13
UVLO GATE DRIVERS AND ANTI-CROSS CONDUCTION IZERO COMPARATOR SWBK 4 L1 3.3H VBUCK 0.6V TO 5V
RUNLDO RUNBK 8 OFF ON 4M SHUTDOWN
SHUTDOWN LOGIC
SHUTDOWN
CLK TSD LOGIC
PGBK 6
0.55V GND PAD 7 PGND
+ -
PWM
+ -
SLOPE COMPARATOR
+ -
+ -
SOFT-START
+ -
1.5MHz OSC
CLK
LOGIC
ERROR AMPLIFIER/ SLEEP COMPARATOR FB 1.2V TSD ISET
100mA
- +
ILIM
ERROR AMPLIFIER
GATE CONTROL 4M
IPK COMPARATOR
ILIM REF ISENSE
ISENSE
+ -
VLDO 3 VLDO 0.6V TO 5V R4 FBLDO 11 0.6V RUNLDO 10 OFF ON VINBK 5 FROM VBST, VBATT1 OR VBATT2 CIN 4.7F R3 COUT 1F
+ -
- +
R6 COUT 4.7F R5 ERROR AMPLIFIER FBBK 9 0.6V
+ -
3100 BD
3100fa
11
LTC3100 OPERATION
The LTC3100 includes an 700mA synchronous step-up (boost) converter, a 250mA synchronous step-down (buck) converter and a 100mA low dropout (LDO) linear regulator housed in a 16-lead 3mm x 3mm QFN package. Both converters utilize current mode PWM control for exceptional line and load regulation and operate from the same 1.5MHz oscillator. The current mode architecture with adaptive slope compensation also provides excellent transient load response, requiring minimal output filtering. Both converters have internal soft-start and internal loop compensation, simplifying the design process and minimizing the number of external components. With its low RDS(ON) and low gate charge internal MOSFET switches and synchronous rectifiers, the LTC3100 achieves high efficiency over a wide range of load current. Burst Mode operation maintains high efficiency at very light loads, but can be disabled for noise-sensitive applications. With separate power inputs for the boost and buck converters, along with independent enable and power good functions, the LTC3100 is very flexible. The two converters can operate from the same input supply, or from two different sources, or can even be cascaded by powering the buck converter from the output of the boost converter. By using the LDO as well, three different output voltages can be generated from a single alkaline/NiMH cell (or the LDO can be used for power sequencing the boost output). Operation can be best understood by referring to the Block Diagram. BOOST CONVERTER Low Voltage Start-Up The LTC3100 boost converter includes an independent start-up oscillator designed to start up at an input voltage of 0.65V (typical). Soft-start and inrush current limiting are provided during start-up, as well as in normal mode. When either VINBST or VBST exceeds 1.4V (typical), the IC enters normal operating mode. Once the output voltage exceeds the input by 0.24V, the IC powers itself from VBST instead of VINBST. At this point, the internal circuitry has no dependency on the input voltage, eliminating the requirement for a large input capacitor. The limiting factor for the application becomes the ability of the power source to supply sufficient energy to the output at low input voltages, and maximum duty cycle of the converter, which is clamped at 90% (typical). Note that at low input voltages, even small input voltage drops due to series resistance become critical, and greatly limit the power delivery capability of the converter. LOW NOISE FIXED FREQUENCY OPERATION Soft-Start The internal soft-start circuitry ramps the peak boost inductor current from zero to its peak value of 700mA in approximately 800s, allowing start-up into heavy loads. The soft-start circuitry is reset in the event of a commanded shutdown or an overtemperature shutdown. Oscillator An internal oscillator sets the switching frequency to 1.5MHz. The oscillator allows a maximum duty cycle of 90% (typical) for the boost converter. Shutdown The boost converter is shut down by pulling the RUNBST pin below 0.3V, and activated by pulling the RUNBST pin above 0.9V. Note that RUNBST can be driven above VIN or VOUT, as long as it is limited to less than the absolute maximum rating. Error Amplifier The error amplifier is a transconductance type. The non-inverting input is internally connected to the 1.20V reference and the inverting input is connected to FBBST. Clamps limit the minimum and maximum error amp output voltage for improved large signal transient response. Power converter control loop compensation is provided internally. A voltage divider from VBST to ground programs the output voltage (via FBBST) from 1.5V to 5.25V, according to the formula: R2 VBST = 1 . 20 V * 1 + R1
3100fa
12
LTC3100 OPERATION
Current Sensing Lossless current sensing converts the peak current signal of the N-channel MOSFET switch into a voltage which is summed with the internal slope compensation. The summed signal is compared to the error amplifier output to provide a peak current control command for the PWM. Current Limit The current limit comparator shuts off the N-channel MOSFET switch once its threshold is reached. Peak switch current is no less than 700mA, independent of input or output voltage, unless VOUT falls below 1V, in which case the current limit is cut in half to minimize power dissipation into a short-circuit. Slope Compensation Current mode control requires the use of slope compensation to prevent subharmonic oscillations in the inductor current waveform at high duty cycle operation. This is accomplished internally on the LTC3100 through the addition of a compensating ramp to the current sense signal. The LTC3100 performs current limiting prior to addition of the slope compensation ramp and therefore achieves a peak inductor current limit that is independent of duty cycle. Zero Current Comparator The zero current comparator monitors the boost inductor current to the output and shuts off the synchronous rectifier once this current reduces to approximately 30mA. This prevents the inductor current from reversing in polarity, improving efficiency at light loads. Synchronous Rectifier To control inrush current and to prevent the inductor current from running away when VOUT is close to VIN , the P-channel MOSFET synchronous rectifier is only fully enabled when VOUT > (VIN + 0.24V). Anti-Ringing Control The anti-ring circuitry connects a resistor across the boost inductor to prevent high frequency ringing on the SW pin during discontinuous current mode operation. The ringing of the resonant circuit formed by L and CSW (capacitance on SWBST pin) is low energy, but can cause EMI radiation. PGOOD Comparator The PGBST pin is an open-drain output which indicates the status of the boost converter output voltage. If the boost output voltage falls 8% below the regulation voltage, the PGBST open-drain output will pull low. The output voltage must rise 3% above the falling threshold before the pulldown will turn off. In addition, there is a 60s (typical) deglitching delay in order to prevent false trips due to voltage transients on load steps. The PGBST output will also pull low if the boost converter is disabled. The typical PGBST pull-down switch resistance is 13 when VBST or VINBST equals 3.3V. Output Disconnect The LTC3100 boost converter is designed to allow true output disconnect by eliminating body diode conduction of the internal P-channel MOSFET rectifier. This allows for VOUT to go to 0V during shutdown, drawing no current from the input source. It also allows for inrush current limiting at turn-on, minimizing surge currents seen by the input supply. Note that to obtain the advantages of output disconnect, there must not be an external Schottky diode connected between SWBST and VBST. The output disconnect feature also allows VOUT to be pulled high without any reverse current into the battery. VIN > VOUT Operation The LTC3100 boost converter will maintain voltage regulation even when the input voltage is above the desired output voltage. Note that the output current capability is slightly reduced in this mode of operation. Refer to the Typical Performance Characteristics section. Burst Mode Operation (for Boost and Buck Converters) Burst Mode operation for both converters can be enabled or disabled using the MODE pin. If MODE is grounded, Burst Mode operation is disabled for both the boost and
3100fa
13
LTC3100 OPERATION
buck converters. In this case, both converters will remain in fixed frequency operation, even at light load currents. If the load is very light, they will exhibit pulse-skip operation. If MODE is raised above 0.9V, or left open, Burst Mode operation will be enabled for both converters. In this case, either converter may enter Burst Mode operation at light load, and return to fixed frequency operation when the load current increases. Refer to the Typical Performance Characteristics section to see the output load Burst Mode threshold vs VIN and VOUT. The two converters can enter or leave Burst Mode operation independent of each other. In Burst Mode operation, each converter still switches at a frequency of 1.5MHz, using the same error amplifier and loop compensation for peak current mode control. This control method eliminates any output transient when switching between modes. In Burst Mode operation, energy is delivered to the output until it reaches the nominal regulation value, then the LTC3100 transitions to sleep mode where the outputs are off and the LTC3100 consumes only 15A of quiescent current from VBST. Once the output voltage has drooped slightly, switching resumes again. This maximizes efficiency at very light loads by minimizing switching and quiescent losses. Burst Mode operation output ripple is typically 1% peak-to-peak. Burst Mode operation for the boost converter is inhibited during start-up, and until soft-start is complete and VBST is at least 0.24V greater than VINBST. Short-Circuit Protection The LTC3100 output disconnect feature allows output short-circuit while maintaining a maximum internally set current limit. To reduce power dissipation under shortcircuit conditions, the boost peak switch current limit is reduced to 400mA (typical). Schottky Diode Although it is not required, adding a Schottky diode from SWBST to VBST will improve efficiency by about 2%. Note that this defeats the boost output disconnect and shortcircuit protection features. BUCK CONVERTER OPERATION The buck converter provides a high efficiency, lower voltage output and supports 100% duty cycle operation to extend battery life. The buck converter uses the same 1.5MHz oscillator used by the boost converter. PWM Mode Operation When the MODE pin is held low, the LTC3100 buck converter uses a constant-frequency, current mode control architecture. Both the main (P-channel MOSFET) and synchronous rectifier (N-channel MOSFET) switches are internal. At the start of each oscillator cycle, the P-channel switch is turned on and remains on until the current waveform with superimposed slope compensation ramp exceeds the error amplifier output. At this point, the synchronous rectifier is turned on and remains on until the inductor current falls to zero or a new switching cycle is initiated. As a result, the buck converter operates with discontinuous inductor current at light loads which improves efficiency. At extremely light loads, the minimum on-time of the main switch will be reached and the buck converter will begin turning off for multiple cycles (pulse-skipping) in order to maintain regulation. Burst Mode Operation When the MODE pin is forced high, or left open, the buck converter will automatically transition between Burst Mode operation at sufficiently light loads (below approximately 10mA) and PWM mode at heavier loads. Burst Mode operation entry is determined by the peak inductor current and therefore the load current at which Burst Mode operation will be entered depends on the input voltage, the output voltage and the inductor value. Typical curves for Burst Mode operation entry threshold are provided in the Typical Performance Characteristics section of this data sheet. The quiescent current on VINBK in Burst Mode operation is only 15A. If the boost converter is enabled and VINBST or VBST are at a higher potential than VINBK, some of the quiescent current will be supplied by the boost converter, reducing the burst quiescent current on VINBK to just 9A.
3100fa
14
LTC3100 OPERATION
Dropout Operation As the input voltage decreases to a value approaching the output regulation voltage, the duty cycle increases toward the maximum on-time. Further reduction of the supply voltage will force the main switch to remain on for more than one cycle until 100% duty cycle operation is reached where the main switch remains on continuously. In this dropout state, the output voltage will be determined by the input voltage less the resistive voltage drop across the main switch and series resistance of the inductor. Slope Compensation Current mode control requires the use of slope compensation to prevent subharmonic oscillations in the inductor current waveform at high duty cycle operation. This is accomplished internally on the LTC3100 through the addition of a compensating ramp to the current sense signal. In some current mode ICs, current limiting is performed by clamping the error amplifier voltage to a fixed maximum. This leads to a reduced output current capability at low step-down ratios. In contrast, the LTC3100 performs current limiting prior to addition of the slope compensation ramp and therefore achieves a peak inductor current limit that is independent of duty cycle. Short-Circuit Protection When the buck output is shorted to ground, the error amplifier will saturate high and the P-channel MOSFET switch will turn on at the start of each cycle and remain on until the current limit trips. During this minimum on-time, the inductor current will increase rapidly and will decrease very slowly during the remainder of the period due to the very small reverse voltage produced by a hard output short. To eliminate the possibility of inductor current runaway in this situation, the buck converter switching frequency is reduced to approximately 375kHz when the voltage on FBBK falls below 0.3V. Soft-Start The buck converter has an internal voltage mode soft-start circuit with a nominal duration of 1.3ms. The converter remains in regulation during soft-start and will therefore
3100fa
respond to output load transients which occur during this time. In addition, the output voltage rise time has minimal dependency on the size of the output capacitor or load current. Error Amplifier and Compensation The LTC3100 buck converter utilizes an internal transconductance error amplifier. Compensation of the feedback loop is performed internally to reduce the size of the application circuit and simplify the design process. The compensation network has been designed to allow use of a wide range of output capacitors while simultaneously ensuring rapid response to load transients. Undervoltage Lockout If the VINBK supply voltage decreases below 1.6V (typical), the buck converter will be disabled. The soft-start for the buck converter will be reset during undervoltage lockout to provide a smooth restart once the input voltage rises above the undervoltage lockout threshold. PGOOD Comparator The PGBK pin is an open-drain output which indicates the status of the buck converter output voltage. If the buck output voltage falls 8% below the regulation voltage, the PGBK open-drain output will pull low. The output voltage must rise 3% above the falling threshold before the pulldown will turn off. In addition, there is a 60s typical deglitching delay in order to prevent false trips due to voltage transients on load steps. The PGBK output will also pull low during overtemperature shutdown and undervoltage lockout to indicate these fault conditions, or if the buck converter is disabled. The typical PGBK pull-down switch resistance is 13 when VINBK = 3.3V. Schottky Diode Although it is not required, adding a Schottky diode from SWBK to the ground plane will improve efficiency by about 2%.
15
LTC3100 OPERATION
LDO REGULATOR OPERATION The LDO regulator utilizes an internal 1.3 (typical) P-channel MOSFET pass device to supply up to 100mA of load current with a typical dropout voltage of 130mV. The input voltage to the LDO is internally connected to the boost output (VBST pin), and can share the same filter capacitor. The LDO can be operated independently of the boost (or buck) converter, providing a sufficient voltage is present on VBST. Soft-Start and Current Limit The LDO has an independent current limit circuit that limits output current to 120mA (typical). To minimize loading on the boost converter output when enabling the LDO, the LDO current limit is soft-started over a 500s period. Therefore the rise time of the LDO output voltage will depend on the amount of capacitance on the VLDO pin. Reverse Current Blocking The LDO is designed to prevent any reverse current from VLDO back to the VBST pin, both in normal operation and in shutdown. If VLDO is pulled above VBST and VBST is above 1V, there will be a small (1A typical) current from VLDO to ground. COMMON FUNCTIONS Oscillator The 1.5MHz oscillator is shared by the boost and buck converters. It will be oscillating if either converter is enabled. If both converters are enabled, the boost N-channel MOSFET switch will be turned on coincident with the buck P-channel MOSFET switch. MODE Control The MODE pin is used to force fixed frequency operation (MODE < 0.3V) or to enable Burst Mode operation (MODE > 0.9V) for both the boost and buck converters. With Burst Mode operation enabled, the two converters will automatically enter or leave Burst Mode operation independently, based on their respective load conditions. There is an internal 1M pull-up on MODE, in the event that the pin is left open. Note: Leaving the pin open, or connecting it to the highest of VINBK or VBST, will result in the lowest Burst Mode quiescent current. Overtemperature Shutdown If the die temperature exceeds 150C (typical) both converters and the LDO regulator will be disabled. All power devices will be turned off and all switch nodes will be high impedance. The soft-start circuits for both converters and the LDO are reset during overtemperature shutdown to provide a smooth recovery once the overtemperature condition is eliminated. Both converters and the LDO will restart (if enabled) when the die temperature drops to approximately 130C.
3100fa
16
LTC3100 APPLICATIONS INFORMATION
PC Board Layout Guidelines The LTC3100 switches large currents at high frequencies. Special care should be given to the PC board layout to ensure stable, noise-free operation. You will not get advertised performance with a careless layout. Figure 1 depicts the recommended PC board layout. A large ground pin copper area will help to lower the chip temperature. A multilayer board with a separate ground plane is ideal, but not absolutely necessary. A few key guidelines follow: 1. All circulating high current paths should be kept as short as possible. Capacitor ground connections should via down to the ground plane in the shortest route possible. The bypass capacitors on all VIN and VOUT pins should be placed as close to the IC as possible and should have the shortest possible paths to ground. 2. To prevent large circulating currents from disrupting the output voltage sensing, the ground for each resistor divider should be returned directly to the ground plane near the IC. 3. Use of vias in the die attach pad of the IC will enhance the thermal environment of the converter, especially if the vias extend to a ground plane region on the exposed bottom surface of the PC board. 4. Keep the connection from the resistor dividers to the feedback pins as short as possible and away from the switch pin connections.
RUNBST 14
PGBST
VINBST
16 SWBST 1 VBST 2 VLDO 3 SWBK 4 5 VINBK
15
MODE 13 12 FBBST 11 FBLDO 10 RUNLDO 9 FBBK 8 RUNBK
LTC3100
6 PGBK
7 GND
VBUCK
3100 F01
Figure 1. Recommended Component Placement for Two-Layer PC Board
3100fa
17
LTC3100 APPLICATIONS INFORMATION
COMPONENT SELECTION Boost Output Voltage Programming The boost output voltage is set by a resistive divider according to the following formula: R2 VOUT = 1 . 200 V * 1 + R1 The external divider is connected to the output as shown in the Block Diagram. A feedforward capacitor may be placed in parallel with resistor R2 to improve the noise immunity of the feedback node, improve transient response and reduce output ripple in Burst Mode operation. A value of 33pF will generally suffice. Boost Inductor Selection The LTC3100 boost converter can utilize small surface mount and chip inductors due to the fast 1.5MHz switching frequency. Inductor values between 2.2H and 4.7H are suitable for most applications. Larger values of inductance will allow slightly greater output current capability by reducing the inductor ripple current. Increasing the inductance above 10H will increase size while providing little improvement in output current capability. The minimum boost inductance value is given by: L> Where: RIPPLE = Allowable Inductor Current Ripple (Amps Peakto-Peak) VIN(MIN) = Minimum Input Voltage VOUT(MAX) = Maximum Output Voltage The inductor current ripple is typically set for 20% to 40% of the maximum inductor current. High frequency ferrite core inductor materials reduce frequency dependent power losses compared to cheaper powdered iron types, improving efficiency. The inductor should have low DCR (series resistance of the winding) to reduce the I2R power losses, and must not saturate at peak inductor current levels. Molded chokes and some chip inductors usually VIN(MIN) * VOUT(MAX ) - VIN(MIN) 1 . 5 * RIPPLE * VOUT(MAX ) do not have enough core area to support the peak inductor currents of 800mA seen on the LTC3100. To minimize radiated noise, use a shielded inductor. See Table 1 for suggested components and suppliers.
Table 1. Recommended Boost Inductors
VENDOR Coilcraft (847) 639-6400 www.coilcraft.com Coiltronics FDK Murata www.murata.com Sumida (847) 956-0666 www.sumida.com Taiyo-Yuden www.t-yuden.com TDK www.tdk.com Toko (408) 432-8282 www.tokoam.com Wurth (201) 785-8800 www.we-online.com PART/STYLE LPS4012, LPS4018 MSS4020, MSS5131 SD14, SD3814, SD3118 MIPSA2520 MIPW3226 LQH43C CDRH2D18, CDRH2D16 CDRH3D14, CDRH3D16 CDRH4D14, CDRH4D16 NR3015 NP03SB VLP VLF VLCF , D518LC D52LC DP418C WE-TPC Type S, M
(
)
Boost Input and Output Capacitor Selection The internal loop compensation of the LTC3100 boost converter is designed to be stable with output capacitor values of 4.7F or greater. Low ESR (equivalent series resistance) capacitors should be used to minimize the output voltage ripple. Multilayer ceramic capacitors are an excellent choice as they have extremely low ESR and are available in small footprints. A 4.7F to 10F output capacitor is sufficient for most fixed frequency applications. For applications where Burst Mode operation is enabled, a minimum value of 20F is recommended. Larger values may be used to obtain very low output ripple and to improve transient response. X5R and X7R dielectric materials are preferred for their ability to maintain capacitance over wide voltage and temperature ranges. Y5V types should not be used. Case sizes smaller than 0805 are not recommended due to their increased DC bias effect.
3100fa
18
LTC3100 APPLICATIONS INFORMATION
Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. It follows that ceramic capacitors are also a good choice for input decoupling and should be located as close as possible to the device. A 2.2F input capacitor on the VINBST pin is sufficient for most applications. Larger values may be used without limitations. For applications where the power source is more than a few inches away, a larger bulk decoupling capacitor is recommended on the input to the boost converter. Table 2 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers directly for detailed information on their selection of capacitors. Note that even X5R and X7R type ceramic capacitors have a DC bias effect which reduces their capacitance with a DC voltage applied. This effect is particularly bad for capacitors in the smallest case sizes. Consult the manufacturer's data for the capacitor you select to be assured of having the necessary capacitance in your application.
Table 2.Capacitor Vendor Information
SUPPLIER AVX Murata Taiyo-Yuden TDK PHONE (803) 448-9411 (714) 852-2001 (408) 573-4150 (847) 803-6100 WEB SITE www.avxcorp.com www.murata.com www.t-yuden.com www.component.tdk.com
can be calculated via the following expression, where f represents the switching frequency in MHz: L= 1 f IL V * 1 - OUT ( H) VIN
A reasonable choice for ripple current is IL = 100mA which represents 40% of the maximum 250mA load current. The DC current rating of the inductor should be at least 450mA to avoid saturation under overload or short-circuit conditions. To optimize efficiency the inductor should have a low series resistance. In particularly space restricted applications it may be advantageous to use a much smaller value inductor at the expense of larger ripple current. In such cases, the converter will operate in discontinuous conduction for a wider range of output loads and efficiency will be reduced. In addition, there is a minimum inductor value required to maintain stability of the current loop (given the fixed internal slope compensation). Specifically, if the buck converter is going to be utilized at duty cycles over 40%, the inductance value must be at least LMIN as given by the following equation: LMIN = 2.5 * VOUT (H) Table 3 depicts the minimum required inductance for several common output voltages.
Table 3.Buck Minimum Inductance
OUTPUT VOLTAGE 0.6V 0.8V 1.2V 2V 2.7V 3.3V MINIMUM INDUCTANCE 1.5H 2H 3H 5H 6.8H 8.3H
Buck Inductor Selection The choice of buck inductor value influences both the efficiency and the magnitude of the output voltage ripple. Larger inductance values will reduce inductor current ripple and will therefore lead to lower output voltage ripple. For a fixed DC resistance, a larger value inductor will yield higher efficiency by lowering the peak current to be closer to the average. However, a larger value inductor within the same family will generally have a greater series resistance, thereby offsetting this efficiency advantage. Given a desired peak to peak current ripple, IL , the required inductance
Larger values of inductor will also provide slightly greater output current capability before reaching current limit (by reducing the peak-to-peak ripple current).
3100fa
19
LTC3100 APPLICATIONS INFORMATION
Table 4. Recommended Buck Inductors
VENDOR Coilcraft (847) 639-6400 www.coilcraft.com Coiltronics FDK Murata www.murata.com Sumida (847) 956-0666 www.sumida.com Taiyo-Yuden www.t-yuden.com TDK www.tdk.com Toko (408) 432-8282 www.tokoam.com Wurth (201) 785-8800 www.we-online.com PART/STYLE LPS3008, LPS3010, LPS3015
the value of the feedforward capacitor in parallel with the upper resistor divider resistor. Note that even X5R and X7R type ceramic capacitors have a DC bias effect which reduces their capacitance with a DC voltage applied. This effect is particularly bad for capacitors in the smallest case sizes. Consult the manufacturer's data for the capacitor you select to be assured of having the necessary capacitance in your application.
Table 5. Buck Output Capacitor Range
VOUT 0.6V 0.8V 1.2V 1.8V 2.7V 3.3V CMIN 15F 15F 10F 6.8F 6.8F 6.8F CMAX 300F 230F 150F 90F 70F 50F
SD3114, SD3118, SD3112 MIPF2016 MIPF2520, MIPS2520 LQH32C LQM31P CDRH2D11, CDRH2D09 CMD4D06-4R7MC CMD4D06-3R3MC NR3010, NR3012 VLF3010, VLF3012 LEMC3225, LBC2518 D3010 DB3015 D312, D301F WE-TPC Type XS, S
Buck Input Capacitor Selection The VINBK pin provides current to the buck converter power switch and is also the supply pin for the buck's internal control circuitry. It is recommended that a low ESR ceramic capacitor with a value of at least 4.7F be used to bypass this pin. The capacitor should be placed as close to the pin as possible and have a short return to ground. For applications where the power source is more than a few inches away, a larger bulk decoupling capacitor is recommended. Buck Output Voltage Programming The output voltage is set by a resistive divider according to the following formula: R6 VOUT = 0 . 600 V * 1 + R5 The external divider is connected to the output as shown in the Block Diagram. It is recommended that a feedforward capacitor be placed in parallel with resistor R6 to improve the noise immunity of the feedback node and reduce output ripple in Burst Mode operation. A value of 10pF will generally suffice.
Buck Output Capacitor Selection A low ESR output capacitor should be utilized at the buck output in order to minimize voltage ripple. Multilayer ceramic capacitors are an excellent choice as they have low ESR and are available in small footprints. In addition to controlling the output ripple magnitude, the value of the output capacitor also sets the loop crossover frequency and therefore can impact loop stability. There is both a minimum and maximum capacitance value required to ensure stability of the loop. If the output capacitance is too small, the loop crossover frequency will increase to the point where switching delay and the high frequency parasitic poles of the error amplifier will degrade the phase margin. In addition, the wider bandwidth produced by a small output capacitor will make the loop more susceptible to switching noise. At the other extreme, if the output capacitor is too large, the crossover frequency can decrease too far below the compensation zero and also lead to degraded phase margin. Table 5 provides a guideline for the range of allowable values of low ESR output capacitors. Larger value output capacitors can be accommodated provided they have sufficient ESR to stabilize the loop or by increasing
3100fa
20
LTC3100 APPLICATIONS INFORMATION
LDO Output Capacitor Selection The LDO is designed to be stable with a minimum 1F output capacitor. No series resistor is required when using low ESR capacitors. For most applications, a 2.2F ceramic capacitor is recommended. Larger values will improve transient response, and raise the power supply rejection ratio (PSRR) of the LDO. Refer to the Typical Performance Characteristics for the allowable range of output capacitor to ensure loop stability. LDO Output Voltage Programming The output voltage is set by a resistive divider according to the following formula: R4 VOUT = 0 . 600 V * 1 + R3 The external divider is connected to the output as shown in the Block Diagram. For improved transient response, a feedforward capacitor may be placed in parallel with resistor R4.
TYPICAL APPLICATIONS
Single-Cell Boost and Buck with Voltage Sequencing
L1 3.3H VBATT 0.9V TO 1.5V 1 5 SWBST VINBK VINBST LTC3100 VLDO FBLDO FF EN_BURST OFF ON 13 14 10 8 MODE RUNBST RUNLDO RUNBK GND 7 BOOST_GOOD BUCK_GOOD SWBK 4 9 3 11 L2 3.3H R4 115k R3 25.5k C2 2.2F 120mA AT VBATT = 0.9V 220mA AT VBATT = 1.2V V_CORE = 1.2V R6 1M R5 1M C3 10F R7 1M R8 1M 2 VBST FBBST 3.5V R2 1M R1 523k +3.3V AT 50mA V_I/O C1 10F 2 VBST, 1V/DIV VI/O, 1V/DIV
Output Voltages During Soft-Start for Sequenced Converter
16 CIN 2.2F
12
+
VCORE, 1V/DIV
1ms/DIV
3100 TA02b
FBBK 15 PGBST 16 PGBK
3100fa
21
LTC3100 TYPICAL APPLICATIONS
Li-Ion Input, Triple Output Converter
100
+5V AT 200mA VBOOST
Efficiency vs Load Current
1000
L1 3.3H VIN 2.5V TO 5V Li-Ion CIN 4.7F 1 5 SWBST VINBK VINBST 2 VBST FBBST R2 2M R1 634k VLDO LTC3100 FBLDO 13 14 10 8 MODE RUNBST RUNLDO RUNBK GND 7 SWBK FBBK 4 9 11 L2 4.7H CFF2 10pF 3 R4 115k R3 25.5k C2 2.2F C1 10F 2 +3.3V AT 50mA V_I/O
90 80 EFFICIENCY (%) 70 60 50 40 30 20
VIN = 3.6V
100 POWER LOSS (mW)
16
12
10
1
BOOST LDO BUCK
OFF ON OFF ON OFF ON
+1.8V AT 250mA V_CORE C3 10F R7 100k R8 100k BOOST_GOOD BUCK_GOOD
10 0 0.01
R6 976k R5 487k
1.8V BUCK 0.1 5V BOOST BUCK POWER LOSS BOOST POWER LOSS 0.01 0.1 1 10 100 1000 LOAD CURRENT (mA)
3100 TA03b
15 PGBST 16 PGBK
3100 TA03a
Single-Cell/Two-Cell or USB Input to 3.3V/1.8V Converter
USB INPUT MBR0520 C1 4.7F L1 3.3H 1 5 SWBST VINBK VINBST 2 VBST FBBST R1 1.07M R2 324k R5 200k R6 100k L2 10H C3 10F R3 301k 1.8V AT 50mA C4 2.2F VLDO 3.3V AT: 100mA FOR VBATT = 1.2V 300mA FOR VBATT = 2.4V 250mA FOR USB INPUT C2 10F VOUT
Efficiency vs Load Current
100 90
3.3V OUTPUT
EFFICIENCY (%)
VBATT 0.9V TO 3.3V
80 VIN = 2.4V 70 60 50 40 30 20 10 0 0.01 0.1 1 10 100 LOAD CURRENT (mA) 1000 VIN = 5V USB VIN = 1.2V
16 C4 4.7F
12
VLDO 3 LTC3100 11
FBLDO
13 14 R7 64.9k 10 8 R4 20k
MODE RUNBST RUNLDO RUNBK GND 7
SWBK FBBK PGBST PGBK
4 9 15 16
3100 TA04b
3100 TA04a
3100fa
22
LTC3100 PACKAGE DESCRIPTION
UD Package 16-Lead Plastic QFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1691)
0.70 0.05
3.50
0.05 2.10
1.45 0.05 0.05 (4 SIDES)
PACKAGE OUTLINE 0.25 0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS 0.75 0.05 BOTTOM VIEW--EXPOSED PAD R = 0.115 TYP 15 16 0.40 1 1.45 0.10 (4-SIDES) 2 0.10 PIN 1 NOTCH R = 0.20 TYP OR 0.25 45 CHAMFER
3.00 0.10 (4 SIDES) PIN 1 TOP MARK (NOTE 6)
(UD16) QFN 0904
0.200 REF 0.00 - 0.05 NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2) 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
0.25
0.05
0.50 BSC
3100fa
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
23
LTC3100 TYPICAL APPLICATION
Single-Cell to 1.2V/1.8V Converter
L1 3.3H VBATT 0.9V TO 1.6V 1 5 SWBST VINBK VINBST FBBST VLDO LTC3100 FBLDO 13 14 10 8 MODE RUNBST RUNLDO RUNBK GND 7 SWBK 4 9 11 L2 3.3H 2 VBST 12 3 R4 200k R3 100k C2 2.2F 2.4V R2 1M R1 1M C1 10F 2 EFFICIENCY (%) 100 90 80 70 60 50 40 30 20 1.2V AT: 120mA FOR VBATT = 0.9V 250mA FOR VBATT = 1.2V VBUCK C3 10F R7 100k 10 0 0.01 VIN = 0.9V VIN = 1.2V VIN = 1.5V 0.1 1 10 100 LOAD CURRENT ON VBUCK (mA) 1000
Efficiency vs Load Current (VBUCK)
16
+
CIN 2.2F
1.8V AT 50mA VLDO
OFF ON
R6 1M R5 1M
FBBK 15 PGBST 6 PGBK
3100 TA05a
3100 TA05b
BUCK_GOOD
RELATED PARTS
PART NUMBER LTC3442 LTC3455 LTC3456 LTC3520 LTC3522 LTC3527/LTC3527-1 LTC3530 LTC3532 LTC3537 LTC3538 LTC3544/LTC3544B LTC3545 DESCRIPTION 1.2A (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter COMMENTS VIN: 2.4V to 5.5V, VOUT(RANGE): 2.4V to 5.25V, IQ = 35A, ISD < 1A, DFN Package
Dual DC/DC Converter with USB Power Manager and Li-Ion 96% Efficiency, Seamless Transition Between Inputs, IQ = 110A, Battery Charger ISD < 2A, QFN Package 2-Cell Multi-Output DC/DC Converter with USB Power Manager Synchronous 1A Buck-Boost and 600mA Step-Down DC/DC Converter Synchronous 400mA Buck-Boost and 200mA Step-Down DC/DC Converter Dual (400mA/800mA) Synchronous Boost Converter 600mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter 500mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter 600mA (ISW), 2.2MHz Synchronous Boost Converter with 100mA LDO 600mA (IOUT), 2MHz Synchronous Buck-Boost DC/DC Converter 300mA, 200mA x2, 100mA, 2.25MHz Quad Output Synchronous Step-Down DC/DC Converter Triple Output, 3mA x 800mA, 2.25MHz Synchronous Step-Down DC/DC Converter 92% Efficiency, Seamless Transition Between Inputs, IQ = 180A, ISD < 1A, QFN Package VIN: 2.2V to 5.5V, VOUT(MIN) = 0.6V, IQ = 55A, ISD < 1A, 4mm x 4mm QFN Package VIN: 2.4V to 5.5V, VOUT(MIN) = 0.6V, IQ = 25A, ISD < 1A, 3mm x 3mm QFN-16 Package VIN: 0.5V to 5V, VOUT: 1.5V to 5.25V, IQ = 12A, ISD < 2A, 3mm x 3mm QFN Package VIN: 1.8V to 5.5V, VOUT(RANGE): 1.8V to 5.5V, IQ = 40A, ISD < 1A, DFN and MSOP Packages VIN: 2.4V to 5.5V, VOUT(RANGE): 2.4V to 5.25V, IQ = 35A, ISD < 1A, DFN and MSOP Packages VIN: 0.68V to 5V, VOUT(MAX) = 5.5V, IQ = 30A, ISD < 1A, 3mm x 3mm QFN Package VIN: 2.4V to 5.5V, VOUT(RANGE): 1.5V to 5.5V, IQ = 35A, ISD < 1A, DFN Package VIN: 2.25V to 5.5V, VOUT(MIN) = 0.8V, IQ = 70A, ISD < 1A, QFN Package VIN: 2.25V to 5.5V, VOUT(MIN) = 0.6V, IQ = 58A, ISD < 1A, QFN Package
3100fa LT 1108 REV A * PRINTED IN USA
24 Linear Technology Corporation
(408) 432-1900 FAX: (408) 434-0507
1630 McCarthy Blvd., Milpitas, CA 95035-7417
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2008

▲Up To Search▲

Price & Availability of LTC3100

	To Download LTC3100 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .